1. Field of the Invention
The present invention relates to an image-reading apparatus including a gain correction processing portion, and an image-forming apparatus equipped with the image-reading apparatus.
2. Related Art
An image-reading apparatus, for example, is configured to include a light source that radiates light onto an original, and electrical components (imaging elements) that change electrical signals by measuring light reflected from the original, and a variety of other components. The shapes and properties of the variety of other components may vary because sizes may not be appropriate or because of changes that can occur over time. In such a case, variations can develop in image data and the like that are obtained by an image-reading apparatus.
Normally, variations that develop in the image data can be resolved by implementing a correction process that uses software. Image-reading apparatuses are able to provide good quality images by implementing such a correction process. Gain correction that corrects variations in quantity of light in light source components, and shading correction that corrects variations in a quantity of light in one line in a main-scanning direction for reading data are representative correction processes. Gain correction includes the concept of gain adjustment. However, the explanation below will use the term gain correction.
Normally, correction processes includes the processes of comparing a status of the apparatus when implementing a reading operation and a predetermined standard state, calculating correction conditions to compensate for differences, and referencing correction conditions. However, some correction processes take time. Also, some corrections may not always correspond to reading operations.
For example, the shading correction process mentioned above implements a correction process in a short amount of time. For that reason, even if a predetermined measurement is taken and a correction condition is calculated just before (after an image read instruction is input) reading an image, a user is made to wait a short amount of time. For that reason, the user does not feel any unpleasantness toward the image-reading process.
However, depending on the algorithm that implements the correction process, gain correction processes can sometimes take several hundreds of ms. In other words, if the apparatus starts taking predetermined measurements and calculating correction conditions after the user presses a button to start reading (start scanning) (to start reading), the user must wait a long time for the gain correction process to complete to start the reading operation. For that reason, users sometimes experience unpleasantness toward the time lag in the image-reading process.
If time-consuming gain correction processes are started just before the reading process, users will feel irritated or unpleasant.
In contrast, when the apparatus power is switched on, gain correction condition (gain setting values) settings applied by the amplifier (amplifier 15 in AFE14) that amplifies electrical signals output from a color CCD sensor 13 (imaging elements), are implemented for a B/W and a color mode, in that order, and gain setting values are saved in a memory portion 30. Also, this image-reading apparatus is configured to implement a gain correction process by applying gain setting values recorded in the memory portion 30, on electrical signals obtained in a reading process on the image-reading apparatus.
As shown in FIG. 1, output from the imaging elements is at a maximum when the power is switched on, and gradually tapers off thereafter.
Therefore, if gain correction conditions are set when the power is switched on, that gain adjustment condition will deviate from gain condition that should be applied when a reading process is implemented, as with the image-reading apparatus described above. The image-reading apparatus described above applies a correction process on electrical signals that are output from the imaging elements as a gain correction condition that is not in line with the true gain correction conditions.
The result is that an inadequate gain correction effect is sometimes obtained. Also, sometimes there are anomalies in the output images. For example, images that are different from the original are sometimes produced. These kinds of undesirable situations can sometimes occur.